1. Field of the Invention
This invention relates to improved subterranean fluid treatment apparatus and methods for treatment of various materials, including municipal and industrial waste streams. More particularly, the present invention relates to downhole or deep well reaction apparatus and methods for reactive treatment of fluid waste streams, including municipal sludge and industrial waste.
2. Description of the Prior Art
Above ground wet oxidation systems have been in use for several years for the treatment of municipal sludge received from a sewage treatment process with limited success. The above ground wet oxidation systems use high pressure and heat to initiate the wet oxidation reaction, however, the apparatus is not energy efficient and results in only partial oxidation of the sludge; see, for example, U.S. Pat. Nos. 2,665,249 and 2,932,613. Further, because the extreme pressures must be generated by a piston, the apparatus is subject to failure. The above ground wet oxidation processes have not, therefore, replaced the traditional methods of treatment of municipal sludge, which includes aerobic and anaerobic treatment, settling, dewatering, drying, incineration, etc.
Various downhole or deep well fluid treatment systems have been proposed by the prior art, however, the first successful deep well reaction apparatus was built by the assignee of the present application based upon the disclosure in U.S. Pat. No. 4,272,383 of Dr. McGrew, entitled "Method and Apparatus for Effecting Subsurface, Controlled, Accelerated Chemical Reactions", which is assigned to the assignee of the present invention. A downnole fluid treatment system generally includes a plurality of nested pipes which extend vertically into the ground a predetermined depth to establish the desired pressure for treatment of the waste at the reaction temperature. The fluid to be treated is pumped into the vertical reaction pipes to form a hydrostatic column of fluid exerting a pressure sufficient to cause an accelerated reaction rate when the fluid is heated to the reaction temperature. Earlier prior art patents, including U.S. Pat. Nos. 3,449,247, 3,606,999 and 3,853,759, proposed various deep well reaction systems, however, these systems were never built or tested.
The above referenced patent of Dr. McGrew and the otner referenced prior art recognized that it is theoretically possible to substantially fully oxidize municipal and industrial wastes, including municipal sludge, at a deptn of approximately one mile, provided the concentration of the oxidizable material in the municipal sludge is balanced against the oxygen injected into the system. In the actual application of this concept in wet oxidation of municipal sludge, for example, considerable difficulties have been experienced in maintaining the reaction at the desired temperature and pressure to achieve maximum or optimum reduction of the chemical oxidation demand (C.O.D.) of the fluid waste stream. The temperature of the "reaction zone" located adjacent the lower extent of the reaction vessel must be continuously monitored to determine when the system becomes autogenic. Heat must be added to the influent to initiate the reaction. When the reaction becomes autogenic, heat is removed from the system to maintain the temperature of the reaction zone at the desired reaction temperature. The above referenced patent of McGrew proposes a heat exchanger located within the nested tube reaction apparatus for adding or removing heat. This was an important breakthrough, however, temperature sensing means located within the reaction vessel become fouled or otherwise failed making temperature measurement difficult. Thermocouples permanently attached to the pipes within the reaction vessel, required removal of over 5000 feet of reaction apparatus to replace the thermocouples which also became fouled in a relatively short period of time. Further, additional means to control the temperature of the reactants in the reaction vessel have been found desirable.
There are pending several applications for patent relating to improvements in deep well reaction apparatus assigned to the assignee of the present application, the disclosures of which are incorporated herein by reference. For example, U.S. patent application Ser. No. 755,880, filed July 7, 1985, discloses the use of an insulated tubular in the heat exchanger for concentrating the heat adjacent the lower extent of the reaction vessel and limiting heat loss during removal of the heat. U.S. patent application Ser. Nos. 943,409, filed Dec. 19, 1986 and filed Mar. 24, 1986 disclose methods of inhibiting scale build-up and methods for cleaning the system to limit downtime. U.S. patent application Ser. No. 017,659 filed Mar. 24, 1987 discloses a method of continuous treatment in a downhole reaction apparatus wherein boiling is initiated in the upcomer to maintain the system at elevated temperatures.
The need, however, remains for improvements in determining and controlling the temperature of the reaction zone while avoiding fouling of thermocouples and permitting easy replacement of thermocouples when damaged or inoperative.